Tuesday, August 1, 2017

Is weather playing a role in MLB's record-setting home run spike this season?

August 1,2017, 12:37:44PM,EDT

The first few months of the 2017 Major League Baseball season were record-breaking.

In
June, players hit more than 1,100 home runs, more than in any other
month in MLB history. This put the league on track for more than 6,000
home runs by the end of the season, which would smash the record set in
2000.
Experts have yet to decide why the MLB has seen such a
spike this season and a general increase in home runs over the past
three years.
Most potential explanations revolve around aspects
like how baseballs are designed or if players are adjusting their swings
to hit more home runs. Some believe
batters are trying to increase the launch angle of their hits and the
speed of their swings, which should result in more home runs. However,
one topic is already known to impact home run rates in certain areas:
weather.
When
the Colorado Rockies entered the MLB in the 1990s, people immediately
noticed the number of home runs at the Rockies' stadium, Coors Field,
was higher than anywhere else in the league, Alan Nathan, professor
emeritus of physics at the University of Illinois, said.
That was
due to an atmospheric trait, lower air density, which can have a big
influence on ball flight. Lower air density can help balls fly longer
distances. The air is less dense at Coors Field since it sits at an
elevation of 5,200 feet above sea level.
“If I’m comparing Major
League Baseball venues, then the most important difference is the
difference between Denver and everywhere else,” Nathan said. “The Denver
effect is very well known... the elevation plays a big role. It shows
up pretty much immediately.”RELATED:5 ways weather is pivotal in a baseball gameMLB spring training: Which teams play in the worst weather?Experts share nutrition tips for reducing heat illness risk among youth athletes 5 tips runners should know before battling summer heat
Air density has a few major
components. The most influential is elevation, Nathan said, while the
second is temperature. The third, humidity, plays a smaller role.
“People
know, players even know, understand intuitively if nothing else, that
the ball simply does not carry as well in cold weather as it does in
warm weather,” Nathan said. “The temperature effect is not as huge [as
elevation], but it’s a big effect.”
Mace Michaels, a meteorologist
for the Twins, said the players and grounds crew he works with, as well
as long-term baseball fans, tend to acknowledge this trend based on
their own experiences and observations.
“They tend to say the baseball flies better when it’s hotter or more humid,” Michaels said.

The
chart above shows the average number of home runs per game in red and
the average air density in green for when those home runs were hit.
These climate characteristics combine to create conditions less or more favorable for home runs in certain fields. One of Nathan’s studies, for example, looked at how climate conditions affected ball fly distance in Arizona and San Francisco.
“Arizona
is about 1,000 feet higher in elevation than San Francisco and has a
temperature about 17 degrees warmer, both of which contribute to lower
air density and therefore longer distance,” Nathan said. “What would
typically be a 400-foot fly ball would travel about 10 feet farther in
Arizona than it does in San Francisco, and it’s partly elevation, partly
temperature.”
Coors Field now keeps baseballs in a humidor, which
increases the relative humidity at which baseballs are stored and
lowers their "bounciness" while increasing their weight. This was meant
to help balance out the elevation effect, and after the humidor's
implementation, the rate of home runs was cut by 25 percent.
The
Arizona Diamondbacks are also considering the install of a humidor, and
Nathan predicted it could reduce home runs hit at Chase Field by 37
percent, even more than in Coors Field because Phoenix has lower
relative humidity than Denver.
Air density and its contributing
influences are well understood, but wind is anther weather condition
that has a large impact on how far a ball flies. The wind's effect is
especially difficult to measure.
Wind conditions, Michaels and
Nathan said, vary significantly, not just at specific points in time
during a ball game, but also within the field itself. This makes
quantitatively accounting for wind difficult, Nathan said.
“A
direct northwest wind in Target Field doesn’t mean all the balls that
fly into left field will be knocked down," Michaels said.
"The
wind kind of swirls in our park, so it has a huge amount of difference. I
can walk 10 feet in the outfield and have the wind at my face and 10
feet later have the wind at my back,” Michaels said. “I’ve walked out
there in all different types of wind, and you can’t even begin to figure
it out.”
Outdoor fields are particularly exposed to weather
variability since grounds crews don’t have the same ability to control
conditions during a game as indoor fields.
Although
weather conditions have the ability to impact how far baseballs travel,
Nathan said he doubts weather-related effects are responsible for the
uptick in home runs this season.
Instead, he said most researchers
are looking into other variables that affect how a ball flies, such as
the speed at which the ball comes off the bat, the design of the
baseball and the way players swing their bats.
Even when looking
at why some fields are considered more home run-friendly, Nathan said
the explanations are usually not weather or climate related.
Besides
a few notable exceptions like Coors and Chase fields and Globe Life
Park in Arlington, Texas, where summer temperatures can reach the
mid-90s F, home runs in different stadiums are often affected by stadium
characteristic like the size of the field and how fences are built.